In various mechanical parts, importance of a method for reducing frictional energy at a contact portion has been spotlighted more and more in order to improve the driving efficiency. To impart low-frictional and wear-resistant characteristics to such mechanical parts, coating technologies using different carbon-based materials have been used.
In particular, conventional diamond like carbon (DLC) or diamond coating processes are problematic in that they cause coating layer separation when a thick membrane is formed to a thickness of 3 μm or more, provide a very low membrane growth rate, and have poor cost-efficiency.
As a solution to the above-mentioned problems, a process for forming a carbide derived carbon (CDC) layer has been suggested. Such a process for forming a carbon membrane includes reacting carbide ceramics with a halogen gas at high temperature to extract metal or non-metal atoms from the surface of carbide ceramics, thereby forming a residual carbon layer. The thus formed carbon layer is called a CDC layer in general.
As compared to DLC or diamond coating, such a process for forming a CDC layer forms a carbon layer through the extraction of metal or non-metal atoms in carbide ceramics, and thus shows lower residual stress and allows formation of a carbon membrane with an infinite thickness. In addition, since nano-sized crystals having an onion like carbon (OLC), graphite or carbon nanotube structure are present inside a carbon layer having an amorphous or diamond structure, the CDC layer has a significantly low frictional coefficient.
However, in a CDC layer, voids are present on the surface and in the inner part thereof due to the extraction of metal or non-metal atoms. Furthermore, such voids cause degradation of roughness and hardness as compared to a carbon membrane formed by DLC or the like.